The present invention relates to a method for controlling a tank venting valve between an internal combustion engine and a fuel vapor storage unit.
Methods for controlling the regeneration of an intermediate fuel vapor storage unit in internal combustion engines are described in U.S. Pat. No. 4,683,861.
The intermediate fuel vapor storage unit may be implemented in the form of an active charcoal filter. It absorbs fuel vapor evaporating in the fuel tank. The active charcoal filter is regenerated by purging it with air. The purging air flows through the active charcoal filter, where it absorbs fuel, and is supplied to the internal combustion engine in the form of fuel-laden regeneration gas. The regeneration of the active charcoal filter by purging it with air is accomplished, for example, by opening a tank venting valve between the active charcoal filter and the intake manifold of the internal combustion engine. The intake manifold vacuum acts in this case as the driving force for purging the filter via a fresh air opening. The flow of the fuel-laden regeneration gas follows the pressure gradient, reaching the internal combustion engine via the tank venting valve.
According to conventional methods, regeneration occurs only in certain engine operating states. In engines with gasoline direct injection, operation with homogeneous distribution of the air/fuel mixture in the combustion chambers is especially suitable, since the regeneration gas also enters the combustion chambers in the form of a homogeneous mixture of air and fuel.
The lean mode of operation with stratified charge distribution favored in gasoline direct injection engines is less suitable, however, because the premixed regeneration gas interferes with the injection jet-controlled charge stratification.
As described in U.S. Pat. No. 6,012,435, in the case of long-lasting stratified-charge operation, regeneration of the active charcoal filter does not, under some circumstance, occur for a longer period of time if the engine is operated in stratified mode for a longer period of time. If this period exceeds a threshold, the engine switches to homogeneous mode, according to U.S. Pat. No. 6,012,435, to allow regeneration of the active charcoal filter.
Depending on the amount of fuel vapor that has been absorbed by the active charcoal filter prior to regeneration, the filter may be laden with more or less fuel. Consequently, the regeneration gas may contain a greater or smaller amount of fuel following regeneration after a longer inactive tank venting phase.
To equalize the fuel volume that is supplied to the internal combustion engine along with the regeneration gas, the amount of fuel flowing via the injectors is usually reduced.
If the regeneration gas is very rich in fuel at the time regeneration begins, the entire fuel volume supplied to the engine is large enough to produce unwanted HC emissions.
It is an object of the present invention to provide an emission-neutral method for supplying regeneration gas in internal combustion engines with tank venting, thereby reducing unwanted HC emissions, without impairing driving comfort or adversely affecting engine torque. It is another object of the present invention to maximize the purging volume under the given ancillary conditions.
The present invention relates to a method for controlling a tank venting valve between an internal combustion engine and a fuel vapor storage unit, with the stored fuel vapor being supplied from the fuel vapor storage unit to the internal combustion engine when the tank venting valve is open. According to the method, a distinction is made between active and inactive tank venting phases, and, when tank venting is active, the opening state of the tank venting valve is preset by a fuel setting arrangement as a function of first operating parameters of the engine and/or the tank venting system and limited by a purge rate limiting arrangement as a function of second operating parameters, or preset by a purge rate setting arrangement as a function of second operating parameters and/or limited by a flow rate factor as a function of third operating parameters.
According to one example embodiment, the first operating parameters of the engine and/or the tank venting system include values for the speed and at least one of the following operating parameters:
Torque
Necessary fuel mass
Intake air temperature
Mixture composition and
Charge distribution in the combustion chamber
According to another example embodiment, the second operating parameters include the integral value of the mass flow via the tank venting valve.
According to a further example embodiment, the third operating parameters depend at least on the speed and the quotient of the intake manifold pressure and the ambient pressure.
According to a further example embodiment, a distinction is made between the active and inactive tank venting phases, and, if the duration of the inactive tank venting phase exceeds a minimum duration, the opening state of the tank venting valve is temporarily limited in the subsequent active tank venting phase to a value below the value preset by the purge rate limiting arrangement or the purge rate setting arrangement.
The present invention also relates to a method for controlling a tank venting valve between an internal combustion engine and a fuel vapor storage unit, with the stored fuel vapor being supplied from the fuel vapor storage unit to the internal combustion engine when the tank venting valve is open, with the internal combustion engine being coupled with a torque converter whose transmission ratio is changeable during internal combustion engine operation, and in which a torque supplied by the internal combustion engine is temporarily reduced during a change in the transmission ratio, wherein the tank venting valve is temporarily closed upon a change in the transmission ratio and a reduction in the torque supplied by the internal combustion engine.
According to a further example embodiment, the purge rate is defined as a quotient of the mass flow via the tank venting valve and the entire mass flow into the intake manifold.
According to a further example embodiment, the purge rate limitation is canceled if the period during which the reduction was active exceeds a predetermined threshold.
According to a further example embodiment, the purge rate limitation is canceled if a measure of the regeneration gas volume flowing to the engine exceeds a threshold value.
According to a further example embodiment, the above-mentioned measure is formed as a function of the integral of the mass flow via the tank venting valve or as a function of the integral over the purge rate.
According to a further example embodiment, the method is used in an internal combustion engine with gasoline direct injection, with tank venting being limited even if undesirably high lambda deviations occur during active tank venting.
If the internal combustion engine is operated with a stratified charge, according to a further example embodiment, the relative change in the low-pass-filtered lambda setpoint is analyzed; and tank venting is limited on account of unwanted high lambda deviations during active tank venting only if the relative change in the low-pass-filtered lambda setpoint is smaller than a predetermined threshold value.
The present invention also relates to an electronic control device for performing at least one of the methods and example embodiments.
According to the methods, a distinction is made between active and inactive tank venting phases, and, in the case of active tank venting, the purge rate is preset by a fuel setting arrangement as a function of operating parameters of the engine and/or the tank venting system and limited by a purge rate limiting arrangement or preset by a purge rate setting arrangement. If the duration of the inactive tank venting phase exceeds a minimum duration, the purge rate in the subsequent active tank venting phase is temporarily limited to a value below the rate preset by the purge rate limiting arrangement or the purge rate setting arrangement.
The method according to the present invention may prevent a change in the load state of the active charcoal filter that occurred during a long inactive tank venting phase from resulting in an unwanted increase in the entire fuel flow to the internal combustion engine. As a result, it may be possible to avoid an unwanted increase in HC emissions following long inactive tank venting phases without having to reduce the wanted high regeneration rates following shorter inactive tank venting phases.
Because the limitation is only temporary, it may also be possible to avoid unwanted limiting of the regeneration rates during longer active tank venting phases.
On the whole, this encourages a wanted high regeneration rate without increased HC emissions during the transition from inactive to active tank venting.
Example embodiments of the present invention are explained below on the basis of the drawings.